Mangroves may cover just 960ha or less than 1 per cent of Singapore, but that is enough for them to store 450,571.7 tonnes of carbon.
This is equivalent to the annual per capita emissions of 621,089 people, local scientists have found.
This amount is also equivalent to 1,652,096 tonnes of stored carbon dioxide (CO2) or 3.7 per cent of Singapore's national CO2 emissions in 2010.
This ability to soak up carbon dioxide from the atmosphere and store high densities of it has gained mangroves a growing prominence globally for their significant role in protecting the earth from the upheavals of climate change.
On top of that, they act as nurseries for crabs, prawns and fishes, and protect coasts against storms and floods.
Mangroves also store more carbon than any other ecosystem, only second at times to peat swamps, said Assistant Professor Daniel Friess, who co-led the mangrove study by a team of researchers from the National University of Singapore's geography department.
The study, done in late 2014, is a first in calculating the total amount of carbon stored in mangroves across the island and was published in international journal Urban Ecosystems last November.
THE CARBON SPONGE
This has big implications because they store so much carbon. If you destroy the mangrove forest, you release that carbon, which becomes a big issue when we talk about climate change emissions.
ASSISTANT PROFESSOR DANIEL FRIESS, who co-led the mangrove study by a team of researchers from the National University of Singapore's geography department
Its findings give a snapshot of the carbon stock in Singapore mangroves, said Prof Friess. "It reminds us that despite their small size, mangrovesare important on a national scale.''
Using data collected between 2012 and 2014, his team collated the figures from upscaling biomass measurements and extrapolated soil samples that went a metre deep by using data from satellite imagery.
The biomass measurements and soil samples were collected from mangroves in places such as Sungei Buloh, Pulau Ubin and Pulau Semakau.
Prof Friess said the carbon stored in Singapore's mangroves was surprisingly high.
Still, it might be an underestimate as the soil of mangrove forests, which is where they store most carbon, can go as deep as 3m.
The soil samples taken for the study, however, went only 1m deep.
He also noted that other inter-tidal ecosystems like seagrass, and even unvegetated ones, such as sandbars and mudflats, also store carbon. But they store less.
A study done on Chek Jawa in Pulau Ubin found that seagrass stored 138 tonnes of carbon per hectare, while mudflats stored 143 tonnes and sandbars, 124 tonnes.
The mangroves there, on the other hand, stored 497 tonnes per hectare.
The study also notes that Singapore appears to hold more carbon per hectare than average cities with a population of two to six million.
When compared with other cities in the region, Singapore's carbon density is higher than the estimates for cities in Vietnam and North Korea and is similar to those in Seoul, South Korea.
Singapore once had about 7,500ha of mangroves. But land reclamation and reservoir construction have destroyed as much as 90 per cent of it.
In fact, deforestation destroyed 2 per cent of South-east Asia's mangroves between 2000 and 2012, totalling more than 100,000ha. Often, they were cleared to make way for rice and oil palm plantations.
"This has big implications because they store so much carbon. If you destroy the mangrove forest, you release that carbon, which becomes a big issue when we talk about climate change emissions," said Prof Friess.
"But if we protect mangroves or restore mangroves or increase mangrove cover, they are one of the best ways to offset and mitigate climate change because they soak up so much carbon dioxide from the atmosphere."